Monitoring and/or controlling device and process

ABSTRACT

The method of controlling and/or monitoring an optical transmission of message signals over an optical line in a repeater station includes providing a device ( 45 ) for generating further optical secondary signals from the received optical secondary signals without generating a stable optical carrier signal for the secondary signals in the device ( 45 ). This device ( 45 ) includes a hybrid circuit ( 451 ) for splitting the received optical secondary signals to form a first branched optical signal portion and a second branched optical signal portion, an optical monitoring and/or control receiver ( 454 ) for generating control and/or monitoring signals ( 456 ) from the first branched optical signal portion and an optical modulating device ( 458 ) controllable by the control and/or monitoring signals. In this method of controlling and/or monitoring the further optical secondary signals are produced from the second branched optical signal portion in the optical modulating device ( 458 ) under control of the control and/or monitoring signals ( 456 ) while maintaining an optical carrier frequency of the further optical secondary signals equal to that of the optical secondary signals received and the further optical secondary signals are interleaved by time-division or code-division multiplexing.

BACKGROUND OF THE INVENTION

The term “multichannel systems” is understood to mean communicationssystems for common transmission of a plurality of message signals via acommon medium, utilizing common devices. As a rule, they are intendedfor long distances, for which they are especially attractive from both atechnical and an economic standpoint. In these cases, depending on thenature of the signals transmitted, a greater or lesser number ofintermediate regenerators or intermediate amplifiers (hereinafterreferred to by the more general term repeater stations) is neededbetween the source and the sink of the message signals. Multichannelsystems are known from electrical communications technology, in the formof frequency-division multiplexing or carrier frequency systems, and inoptical communications they are known in the form of wavelengthmultiplexing systems.

It is usual in multichannel systems to attach signals of particularfrequencies or wavelengths to message blocks (in electricalfrequency-division multiplexing technology, these attached signals areoften called a pilot tone or pilot frequency; in optical communicationsthey are called a monitoring signal), and these signals take on variousauxiliary tasks, such as that of representing the level state of thetotal band; in this case, the level of these signals is evaluated andused to regulate the level of the total bandwidth, and/or to ascertainthe exceeding of certain impermissible level states, such as a drop inthe level below a predetermined value. However, they can also be used asa carrier signal, for carrying monitoring information onward or fordelivering control instructions to repeater stations. It will readily beappreciated that the two task areas can also be combined; in addition,still other special tasks (such as being utilized as a referencefrequency signal) are also common. All of these monitoring or controlsignals will hereinafter be referred to as secondary signals, in which(temporarily, or on a long-term basis) only one message channel isprovided.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved methodand an improved device for monitoring and/or control of a transmissionroute for messages over optical wave guides.

This object, and others which will be made more apparent hereinafter,are attained in a method for controlling and/or monitoring atransmission route for message transmission over optical waveguides,wherein the transmission route includes at least one repeater stationthat receives optical secondary signals, serving as monitoring and/orcontrol signals, within an optical transmission channel from a precedingor upstream portion of the transmission route in a transmissiondirection and generates further optical secondary signals to betransmitted over a portion of the transmission route following the atleast one repeater station in the transmission direction within theoptical transmission channel.

According to the invention, the further optical secondary signals to betransmitted over the portion of the transmission route following the atleast one repeater station are formed by optical modulation of thereceived optical secondary signals in a device provided in the at leastone repeater station.

According to the invention the monitoring and/or control device in arepeater station in the transmission route for message transmission overthe optical waveguides comprises means for connection to a portion ofthe transmission route on an input side thereof for receiving opticalsecondary signals acting as monitoring and/or control signals, means forconnection to a following portion of the transmission route on an outputside thereof for transmitting further optical secondary signals actingas further monitoring and/or control signals, and an optical modulatorincluding means for modulating the optical secondary signals received onthe input side to form the further optical secondary signals for furthertransmission.

The invention makes it possible to implement a monitoring and/or controlchannel for optical multichannel systems with amplifying repeaterstations in an especially simple, economical way. All the essential,usual and known tasks of such monitoring and/or control channels can beperformed. By means of the invention, the generation of stable opticalcarrier signals (which is considerably more complicated and expensivethan the corresponding generation of stable electrical carrier signals)in repeater stations can be dispensed with.

BRIEF DESCRIPTION OF THE DRAWING

The objects, features and advantages of the invention will now beillustrated in more detail with the aid of the following description ofthe preferred embodiments, with reference to the accompanying figures inwhich:

FIG. 1 is a block diagram of a device used for performing the method forcontrolling and/or monitoring a transmission route for messagetransmission over optical waveguides;

FIG. 2 is a time-division multiplexing diagram for the device shown inFIG. 1;

FIG. 3 is a block diagram of a multichannel system for opticaltransmission of messages in which the device of FIG. 1 is used;

FIG. 4 is a frequency or wavelength diagram of an example of amultichannel system including five message channels and one monitoringand/or control channel; and

FIG. 5 is a block diagram of a processing device including the device ofFIG. 1.

DESCRIPTION OF AN EXEMPLARY EMBODIMENT

FIG. 3 shows an optical line connection of a multichannel system with anoptical waveguide 10 as the connection between a terminal device 20 anda terminal device 30 (counterpart terminal point), with repeaterstations 40 and 50 disposed between them; in practice, the connection istypically bidirectional, while here only one transmission direction isshown. The number of repeater stations is merely an arbitrary example.

FIG. 4 shows a frequency or wavelength diagram of such a system, withsix monitoring channels, with five message channels 1-5 for usefulsignals and one monitoring and/or control channel 11, which isespecially emphasized. The number of monitoring channels is merely anarbitrary example, and the same is true for the relative location of themonitoring and/or control channel 11 with regard to the messagechannels.

FIG. 5 shows a device 41 for separate frequency- or wavelength-selectiveprocessing of certain monitoring channels of the total bandwidth(channel blocks) of FIG. 4, comprising an input filter combination 42,an output filter combination 43, and separate, intervening devices,namely a device 44 for the main transmission band, comprising themessage channels 1-5, on the one hand and another device 45 for themonitoring and control channel 11 on the other.

The frequency range of FIG. 4 is formed in the terminal device 20 (FIG.3) and is transmitted to the counterpart terminal point via the repeaterstations 40 and 50. In the monitoring and control channel 11, apermanently applied optical carrier signal with an amplitude equal to orsystematically less than the amplitudes in the optical message channels1-5 is preferably transmitted as the secondary signal. In FIG. 5, oneprocessing device 41 is provided in each of the repeater stations.Devices 44 for the message channels 1-5 are each connected to inputs 431of output filter combinations 43 and can have either optical dampingelements for level adaptation of the various routes or more-complexdevices, such as distortion suppression circuits to compensate forfrequency or phase drifting, dispersion, or the like. They will not bediscussed in further detail here; what is important is only that theirdamping is adapted to the damping of the route via a device 45 for themonitoring and/or control channel. Otherwise, essentially to compensatefor the line damping of the line segment preceding them, the repeaterstations 40 and 50 include optical amplifiers 46 (shown in dashed linesin FIG. 5) in the form of optical-fiber amplifiers, which are insertedeither upstream or downstream of the processing device 41, or in splitfashion both upstream and downstream of it, in the transmission routeand are capable of transmitting signals over the total bandwidth of FIG.4, including the monitoring and/or control channel 11.

The devices 45 perform various subsidiary tasks. FIG. 1 illustrates theprinciple. First, there is a first hybrid circuit 451, which splits thesecondary signal of the monitoring and control channel into two paths452 and 453. An optical monitoring and control receiver 454 is connectedto the path 452 and in a known manner it converts the secondary signalinto an electrical signal, amplifies it, and evaluates it in anevaluation circuit 455. The evaluation can include the most variouskinds of typical subsidiary tasks, such as monitoring for impermissiblelevel deviations, or deriving a control signal 457 for closed-loopcontrol of the gain of the amplifier 454, or both. The monitoring andcontrol receiver 454 may also, in a known manner, output an electricalor optical signal as a reference frequency, for example to other devicesin more-complex repeater stations that have additional tasks (such asadding or dropping partial blocks). From the applicable repeaterstation, the evaluation circuit 455 can be supplied with signals whichare needed for comparison purposes and/or are carried onward over a line456 (for instance in the form of a multiplex data stream, including withauxiliary carriers).

From the secondary signal, the partial signal on path 453 is fed backinto the output filter combination 43 (input 432) via a furtherprocessing device 458. According to the invention, the processing device458 comprises a device for modulating optical signals. This device maybe either a passive, damping modulator, for instance in the form of anabsorption modulator or a Mach-Zehnder interferometer, or a suitablymodulatable active, amplifying modulator, for example in the form of anoptical semiconductor amplifier or an optical-fiber amplifier. Inaddition to intensity modulation, other types of modulation are alsopossible. By means of this arrangement, the need for especiallygenerating a highly stable optical carrier in the repeater stations isaverted.

The mode of operation of the processing device 458 is such that with thesignals on the lines 453 and 456, an optical multiplexing signal(time-division multiplexing, frequency-division multiplexing or othertype of multiplexing signal) is generated for the input 432,specifically while keeping the carrier frequency present on the line 453of the monitoring and control channel 11 unchanged.

If the filtered-out secondary signal has already been modulated, andthis modulation is to be retained, then the modulator must also besynchronized. The carrier signal, modulated for the first time oradditionally modulated in this way, is then carried via further repeaterstations (of which only repeater station 50 is shown here) to thedistant counterpart end point 30, where it is evaluated. To enableseparate evaluation of the monitoring and control signals of differentrepeater stations, a suitable multiplexing and especially time-divisionmultiplexing plan can be used; by way of example, this can be embodiedas in FIG. 2, in such a form that each repeater station, in the order inwhich the repeater station is placed in the transmission route, attachesa new signal packet 63, 64, 65, etc. to an existing secondary signalpacket 60 (of duration 61) that is transmitted by the terminal device 20and has a header signal 62 that is repeated at certain regularintervals. Methods for doing so are known and can easily be implementedelectronically. The corresponding evaluation circuits are then part ofthe respective evaluation arrangement 455. In principle, an arbitrarynumber of further repeater stations can be included; each repeaterstation is equipped not only with the amplifiers 46 but also with thedescribed devices 41 (FIG. 5).

In short, the mode of operation of a preferred exemplary embodiment ofthe invention can be summarized as follows, in conjunction with FIG. 1:

In a fiber-optical communications system, to make it easy to carrycontrol and/or monitoring signals as secondary signals in a controland/or monitoring channel, in intermediate regenerators and/orintermediate amplifiers of a transmission route the secondary signalsare filtered out of the total bandwidth and in a device 45, whilekeeping the optical carrier frequency unchanged, are optically modulatedin a modulator 458 by means of further secondary signals (which canoptionally be combined into a multiplex signal) that are carried over aline 456. The outcome of this signal processing is returned to thetransmission route again at the output of the intermediate regeneratoror intermediate amplifier.

What is claimed is:
 1. A method of controlling and/or monitoring anoptical transmission of message signals over an optical line, saidoptical line comprising at least one optical repeater station (40, 50)connected between optical wave guides (10), said method comprising thesteps of: a) transmitting the message signals and optical secondarysignals acting as monitoring and/or control signals over said opticalline; b) receiving the optical secondary signals in said at least oneoptical repeater station (40, 50) from an upstream portion of saidoptical line; c) optically modulating said optical secondary signalsreceived in step b) in said at least one optical repeater station (40,50) to produce further optical secondary signals to be transmitted overa downstream portion of said optical line; and d) transmitting saidfurther optical secondary signals over said downstream portion of saidoptical line; wherein no optical carrier signals are generated in saidat least one repeater station (40, 50).
 2. The method as defined inclaim 1, wherein the optical modulating of step c) is performedpassively.
 3. The method as defined in claim 1, wherein the opticalmodulating of step c) is performed actively.
 4. The method as defined inclaim 1, wherein the optical modulating of step c) is performed activelyby switching.
 5. A method of controlling and/or monitoring an opticaltransmission of message signals over an optical line, said optical linecomprising at least one optical repeater station (40, 50) connectedbetween optical wave guides (10), said method comprising the steps of:a) transmitting the message signals and optical secondary signals actingas monitoring and/or control signals over said optical line; b)providing said at least one optical repeater station (40, 50) with adevice (45) for generating further optical secondary signals to betransmitted from said at least one repeater station from said opticalsecondary signals received in said at least one optical repeaterstation, said device (45) comprising a hybrid circuit (451) forsplitting the received optical secondary signals, an optical monitoringand/or control receiver (454) for providing control and/or monitoringsignals (456) and an optical modulating device (458) controllable by thecontrol and/or monitoring signals; c) splitting the optical secondarysignals received in the at least one repeater station (40,50) by meansof the hybrid circuit (451) to form a first branched optical signalportion and a second branched optical signal portion; d) providing thecontrol and/or monitoring signals (456) by the optical monitoring and/orcontrol receiver (454) receiving the first branched optical signalportion; and e) producing the further optical secondary signals from thesecond branched optical signal portion in the optical modulating device(458) under control of the control and/or monitoring signals (456) inthe at least one repeater station so as to keep an optical carrierfrequency of said further optical secondary signals to be transmittedequal to that of the optical secondary signals received in the at leastone repeater station (40, 50) and so that the further optical secondarysignals are interleaved by time-division or code-division multiplexing;wherein no optical carrier signals are generated in said at least one ofsaid optical repeater station (40, 50).
 6. A monitoring and/or controldevice in an optical repeater station for monitoring and/or control oftransmission of message signals over an optical line, said monitoringand/or control device including means for receiving optical secondarysignals together with the message signals in the optical repeaterstation; means (45) for generating further optical secondary signals tobe transmitted from the optical repeater station (40,50) from theoptical secondary signals received in the optical repeater station(40,50), said means (45) comprising a hybrid circuit (451) for splittingthe received optical secondary signals to form a first branched opticalsignal portion and a second branched optical signal portion, an opticalmonitoring and/or control receiver (454) for generating control and/ormonitoring signals (456) from the first branched optical signal portionand an optical modulating device (458) controllable by the controland/or monitoring signals (456); means for producing the further opticalsecondary signals from the second branched optical signal portion in theoptical modulating device (458) under control of the control and/ormonitoring signals (456), so that an optical carrier frequency of saidfurther optical secondary signals transmitted over the optical line isequal to that of the optical secondary signals received in the at leastone repeater station (40, 50) and so that the further optical secondarysignals are interleaved by time-division or code-division multiplexing;wherein no optical carrier signals are generated in said at least one ofsaid optical repeater station (40, 50).
 7. The device as defined inclaim 6, wherein said control and/or monitoring signals (456) producedby said optical monitoring and/or control receiver (454) are optical. 8.The device as defined in claim 6, wherein said control and/or monitoringsignals (456) produced by said optical monitoring and/or controlreceiver (454) are electrical.
 9. The device as defined in claim 8,wherein said optical monitoring and/or control receiver (454) comprisesmeans for converting an input optical signal into an electrical signaland means for amplifying the electrical signal.